232 Renews. — Prof. 0. C. Marsh — Ancient Lake-basins. 



rank as formations, include the Glacial Deposits of Boulder-clay, 

 Sand and Gravel ; the Brick-earth and Clay-with-flints on the Chalk 

 tracts ; and the Alluvium, Brick-earth and Gravel of the valley of 

 the Thames and its tributaries. 



Under the term Pebble-gravel are included deposits of pebbly 

 gravel whose age is uncertain ; many such deposits are undoubtedly 

 older than the Boulder-clay, but some of them may possibly be 

 Post-Glacial. 



The country was geologically surveyed by Messrs. H. W. Bristow, 

 W. Whitaker, T. B. Polwhele, E. Trench, W. B. Dawkins, H. B. 

 Woodward, P. J. Bennett, W. A. E. Ussher, J. H. Blake, and C. E. 

 Hawkins. 



II. — Prof. 0. C. Marsh on the Ancient Lake-basins of the 

 Eocky Mountain Begion. 1 



NO fact which has come under our notice bearing upon the 

 antiquity of the great North American Continent, as an " Old 

 Land Area," has appeared to us more wonderful than the discovery 

 in the Bocky Mountain Begion of undoubted evidences of the former 

 existence of a succession of vast fresh-water lakes. The deposits 

 with which each is filled prove them to have been respectively of 

 Eocene, Miocene, and Pliocene age ; the fauna being entirely distinct 

 in each and also quite different from that now existing. 



The one first discovered and best known, called Green Biver Basin, 

 lies between the Bocky Mountains and the Wasatch range, in the 

 depression now drained by the Green Biver. It has the Uintah 

 Mountains for its southern border, and extends north as far as the 

 Wind Biver range. This basin was visited by Professor Marsh in 

 1868, but not fully explored until 1870, when he traced the deposits 

 and determined its Eocene age. From it he has obtained 150 species 

 of extinct vertebrates, corresponding with those of the Paris Basin, 

 some even indicating a still lower horizon. These fresh- water 

 deposits are of enormous thickness, 6000 feet at least ; nearly or quite 

 horizontal, and resting unconformably on the subjacent Cretaceous 

 coal-bearing rocks. 



A second and larger lake existed in Eocene times south of the 

 Uintah Mountains at 2000 feet lower level than the northern lake, 

 and receiving part of its waters from that source. Its deposits 

 were also explored by Prof. Marsh in 1870. 



The fauna entombed in these Eocene lakes is essentially the same, 

 and indicates a tropical climate. This is especially seen in the great 

 number of the remains of Tapiroid mammals, monkeys, crocodiles, 

 lizards, and serpents, discovered by Professor Marsh in these deposits. 



Those of the Dinocerata, the largest of Eocene mammals, have only 

 been found as yet in the northern basin. 



The Miocene (White Biver) Lake-basin appears to have extended 

 south from the Black Hills to the Bepublican Biver, or from the 44th 

 to the 40th parallel of latitude. 



1 See the American Journal of Science and Art, vol. ix. no. 49, p. 49. 



